Association of dietary vitamin C intake with depression in adults: A cross-sectional study of NHANES from 2005 to 2020

Background: The aim of this study was to evaluate the association between dietary vitamin C intake and depression in adults. Methods: This cross-sectional study utilized data from the National Health and Nutrition Examination Survey (NHANES) during 2005 to 2020. Logistic regressions and restricted cubic spline (RCS) regression were used to assess the association between dietary vitamin C intake and depression. Additionally, we performed stratified and sensitivity analyses to evaluate the stability of the results. Results: This study included 38,157 participants, with 3448 (9.04 %) of them experiencing depression. The vitamin C intake was negatively associated with depression after adjusting for all covariates (OR = 0.91, 95%CI: 0.88 -0.94, P < 0.001). Similar inverse associations were observed when vitamin C intake was transformed into categorical variables. Individuals in higher quartiles of dietary vitamin C intake (Q2, Q3, and Q4) had lower odds ratios (ORs) compared to those in the lowest quartile (Q1), as indicated by adjusted ORs of 0.78 (95 % CI: 0.71 -0.87, P < 0.001), 0.74 (95 % CI: 0.67 -0.82, P < 0.001), and 0.73 (95 % CI: 0.65 -0.81, P < 0.001), respectively. The RCS analysis found an L-shaped nonlinear relationship between dietary vitamin C intake and depression, after adjusting for all covariates ( P for non-linearity <0.001). Consumption of vitamin C was inversely associated with depression (OR = 0.994, 95%CI: 0.993 -0.996, P < 0.001) for intakes below 93.61 mg, but there was no association between dietary vitamin C intake and depression ( P = 0.980) for intakes of 93.61 mg or higher. The inverse associations between vitamin C intake and depression remained robust in stratified and sensitivity analyses. Limitations: This study was a cross-sectional study, and therefore unable to establish a causal relationship between dietary vitamin C intake and depression. We are unable to fully eliminate the confounding effects resulted from other unmeasured or unknown factors. Conclusion: The study revealed a negative association between dietary vitamin C intake and depression, as well as an L-shaped nonlinear relationship between vitamin C intake and depression.